Magnetic induction, audiofrequency selective, remote control system

ABSTRACT

A remote control system for models and the like including a transmitter having a magnetic induction loop in which electromagnetic waves are generated and transmitted including desired intelligence. The magnetic induction loop preferably encompasses an area in which remote control is desired whereby on operation of the transmitter an electromagnetic flux of controlled intensity is provided within the area. The remote control system further includes a receiver for receiving the electromagnetic waves from the transmitter magnetically inductively coupled to the transmitter and means for controlling a model in accordance with the output of the receiver.

United States Patent John W. Lemon, Jr.

712 Princeton Road, Berkley, Mich. 48072 [21] Appl. No. 345,380

[22] Filed Feb. 17, 1964 [45] Patented Mar. 9, 1971 72] inventor [54]MAGNETIC TNDUCTION, AUDIOFREQUENCY SELECTIVE, REMOTE CONTROL SYSTEM 3Claims, 6 Drawing Figs.

[52] 11.8. C1 343/225, 46/210, 46/244 [51] lint. U .A63h33/26, 1104b7/00 [50] Field otSearch 317/123, 147; 340/171; 318/16; 325/169;343/202, 225; 179/82; 178/43; 325/37; 340/148 [5 6] References CitedUNITED STATES PATENTS 1,938,379 12/1933 Gerth 325/169 2,742,735 4/1956Somrnerhoff 318/16X 3,022,420 2/1962 Brinkerhoff t 3l8/16X 3,029,3714/1962 Saito 318/16 3,147,407 9/1964 Warner et a1. 317/146 3,176,2293/1965 Pierce 325/169X 3,192,507 6/1965 Sudges 340/171 3,215,912 11/1965Bruno 318/16 3,238,502 3/1966 Babcock.... 340/148 3,271,680 9/1966Reynolds 340/171X 3,047,783 7/1962 Van Oort et a]. 343/225X 3,113,27012/1963 Bassett 340/311X OTHER REFERENCES A Radio-Control System ForModels QST, February l952,pp (Three) l8, 19; Title page, H.W. Lawson,Jr.

Primary Examiner-Donald J. Yusko Attorney-Whittemore, Hulbert & BelknapABSTRACT: A remote control system for models and the like including atransmitter having a magnetic induction loop in which electromagneticwaves are generated and transmitted including desired intelligence. Themagnetic induction loop preferably encompasses an area in which remotecontrol is desired whereby on operation of the transmitter anelectromagnetic flux of controlled intensity is provided within thearea. The remote control system further includes a receiver forreceiving the electromagnetic waves from the transmitter magneticallyinductively coupled to the transmitter and means for controlling a modelin accordance with the output of the receiver.

.Q/ as PATENTEUMAR 9mm 3569,5369

SHEET 2 OF 2 Fl (5.4. I0 I86 97 m0 I08 0 k 72 7 88 6 a2 us INVENTOR.JOHN W.LEMON JR.

BY WXZZZ W j Q ATTORNEYS MAGNETHC INDUCTION, AUDIOFREQUENCY SELIECTEVIE,REMGTE (ZONTROL SYSTEM The invention relates to electromagneticallycoupled transmitters and receivers and refers more specifically to anaudiofrequency selective, magnetic induction coupled short rangecommunication or remote control system or the like.

In the past remote control systems for private use have been seriouslylimited by the crowded nature of the frequency spectrum and the controlof frequencies above audiofrequencies by the Federal CommunicationsCommission.

The usual transmitters and receivers for remote control or communicationsystems have extremely low power output for power input at lowfrequencies. The poor efficiency in terms of power output over powerinput of low frequency trans mitting and receiving systems operating ataudiofrequencies and below is due largely to the length of wavestransmitted at these frequencies and the poor sensitivity to long wavesof the relatively short antennae usually available for transmission andreception thereof.

It is therefore an object to provide a primarily electromagneticallycoupled short range communication or remote control system.

Another object is to provide a primarily electromagnetically coupledsystem as set forth above which is frequency selective.

Another object is to provide a remote control system for a modelautomobile or the like, including a magnetic induction, audio frequencyselective remote control transmitter having an oscillator, a pair ofemitter follower amplifiers and a source of electrical energy with oneof the amplifiers including an elongated magnetic induction looptransmitting element connected in the circuit thereof as a load thereon.

Another object is to provide structure as set forth above wherein meansare provided to pulse the one amplifier to provide discrete signal-onand signal-off times of transmission from said magnetic induction loop.

Another object is to provide transmitter structure as set forth abovewherein the means for pulsing the one amplifier comprises a free runningmultivibrator and means for varying the pulse width thereof.

Another object is to provide a magnetic induction, audiofrequencyselective remote control transmitter including an oscillator, a pair ofemitter follower amplifiers and a source of electrical energy operablyassociated in a transmitting circuit with one of the amplifiersincluding an elongated magnetic induction loop transmitting elementconnected in the circuit thereof as a load thereon.

Another object is to provide a remote control system for a modelautomobile or the like, including a magnetic induction, audiofrequencyselective, remote control receiver having a magnetic induction signalpickup circuit tuned to a selected audio frequency, two audiofrequencyamplifiers, a rectifier and audiofrequency amplifier and a power supplyconnected in receiving circuit with the rectifier and audiofrequencyamplifier including a relay coil in circuit therewith as the loadthereon.

Another object is to provide a magnetic induction, audiofrequencyselective receiver including a magnetic induction signal pickup circuittuned to a selected audiofrequency which circuit includes a coil havinga permeable core operably associated therewith.

Another object is to provide a receiver as set forth above in- 4 cludinga pair of audio amplifiers and a rectifier-amplifier connected across asource of voltage and connected to the magnetic induction pickupcircuit.

Another object is to provide a remote control receiver as set forthabove and further including a relay coil as a load on therectifier-amplifier.

Another object is to provide a remote control system for a modelautomobile wherein a first motor is used to provide the driving forcefor the automobile, a second motor is used to provide steering for theautomobile and a receiver is secured to the automobile for alternatelyenergizing the steering motor in opposite directions in accordance withreception or nonreception of a transmitted control signal.

Another object is to provide an audiofrequency selective, magneticinduction, remote control system which is simple in construction,economical to manufacture and efficient in use.

Other objects and features of the invention will become apparent as thedescription proceeds, especially when taken in conjunction with theaccompanying drawings, wherein:

FIG. I is a diagrammatic representation of a model automobile chassishaving a receiver constructed in accordance with the inventionpositioned thereon.

FIG. 2 is a longitudinal section view of the model automobile chassisillustrated in FIG. I taken substantially on the line 2-2 in FIG. 1.

FIG. 3 is a schematic diagram of the steering motor energizing circuitof the model automobile chassis illustrated in FIGS. l and 2.

FIG. 4 is a schematic diagram of a magnetic induction audiofrequencyselective remote control system transmitter constructed in accordancewith the invention.

FIG. 5 is a schematic diagram of an audiofrequency selective magneticinduction remote control receiver constructed in accordance with theinvention.

FIG. 6 is a schematic diagram of an-electronic pulsing circuit for usein the transmitter illustrated in FIG. 4.

With particular reference to the FIGS. of the drawings, one embodimentof the invention will now be disclosed in detail.

In accordance with the' invention the transmitter 10 produces anelectromagnetic signal at'a selected frequency. The electromagneticsignal produced by the transmitter 10 is received by the receiver 12.Receiver 12 in turn operates relay 54 to energize steering motor 16 ofmodel automobile 18 in one direction. Steering motor 16 is normallyenergized in the opposite direction when no signal is received by thereceiver 12 from the transmitter 10.

Thus in operation the model automobile I8 is caused to move in thedirection of arrow 20 on energizing drive motor 22 and may be steeredthrough drive motor 16 coupled to steering wheel 24 in accordance withwhether or not the steering motor 16 is energized.

Transmitter 10 may be pulsed by the electronic pulsing circuit 26 ifdesired. With the. pulsing circuit 26 in use the direction of steeringof automobile 18 may be changed by varying the position of the wiper arm218 in pulsing circuit 26 if desired, as will be explained in moredetail subsequently.

More specifically the model automobile 18 which it is desired toremotely control, as best shown in FIGS. 1 and2, comprises a frame 30 towhich the driving wheels 32 and 34 are secured by means of axle 36 whichis rotatably mounted on frame 30. Axle 36 is turned through a pulley andflexible belt arrangement 38 from drive motor 22. Drive motor 22 isenergized on closing of switch 40 to connect the batteries 42 to thedrive motor 22.

Steering of the automobile 18 is accomplished through the steering wheel24 secured for rotation to a bracket 44 connected to bellcrank 46.Bellcrank 46 is pivotally secured by pivot pin 48 to chassis 30 and isurged in one direction by spring 31. Bellcrank 46 is also pivotallyconnected to the reciprocally mounted rod 50. Rod 50 is in turnconnected to the arm 52 which is secured to steering motor 16 forrotation between limits therewith.

In operation rod 50 moves longitudinally in one direction in oppositionto spring 31 on energization of the steering motor 16 in one direction.The rod is moved in the opposite direction by spring 311 in conjunctionwith steering motor 16 energized in the opposite direction.Reciprocation of the rod 50 in opposite directions about an axisperpendicular to the chassis 30 due to pivotal movement of bellcrank 46on pivot pin 48. It will be understood that steering motor 16 could beenergized in only one direction with movement of rod 50 in the oppositedirection only by spring 31.

Steering motor 16 is energized in one direction when the relay 54 isenergized. Steering motor i6 is energized in the op positc directionwhen relay 54 is not energized. Such operation will be evident from FIG.3 wherein the connection of the relay 54 to the batteries 56 isillustrated in detail. Thus when the coil 62 of relay 54 is nonenergizedand the armature 58 thereof is in the normal position illustrated,current flows through the motor 16 in the direction of arrow 60. Onenergizing of the coil 62 the motor is energized in the direction ofarrow 64, as illustrated in FIG. 3. Coil 62 of relay 54 is energized inaccordance with whether or not a signal id received by receiver 12 fromtransmitter 10, as will be evident subsequently. I

Transmitter 10, as best shown in FIG. 4, includes the oscillator 66, twoemitter follower power amplifiers 68 and 70 and the power supply 72.Power supply 72 comprises two 1.5 volt batteries 71 and 73 connected inseries.

Oscillator 66 includes the transistor 74 having emitter, base andcollector elements 76, 78 and 80, respectively, emitter resistor 82, avoltage divider network from power supply 72 including resistors 84, 86and 88, feedback coil 90 and tuned circuit 92 including coil 94 andcapacitor 96 in parallel with each other and in series with resistor 84and resistor 97. The emitter resistor 82 limits the amplitude of thesine wave signal from oscillator 66 and provides a high degree oftemperature stability for the oscillator. The voltage divider networkincluding resistors 84, 86 and 88 has a relatively low impedance, as forexample a total of less than one hundred ohms, so that no bypasscapacitor across 88 is necessary.

In accordance with the invention the tuned circuit 92 is adjustable infrequency by means of the tuning capacitor 96 and in the present examplethe circuit 92 is tuned to a predetermined frequency, such as forexample 1.5 kilocycles or 9 kilo cycles.

The emitter follower power amplifier 68 includes the transitor 98 havingemitter 100, base 102 and collector 104 connected as shown in FIG. 4 tothe load resistor 106, the tuned circuit 92 and the power supply 72respectively. Amplifier 68 receives the sine wave signal from tunedcircuit 92, amplifies the power thereof and feeds an output sine wavesignal across load resistor 106 to the base 108 of transistor 110 ofpower amplifier 70.

Transistor 110 includes the emitter 112 and collector 114 in addition tothe base 108. As shown in FIG. 4 the load on the power amplifier 70 isan induction loop 116 formed of one hundred sixty feet of number 24copper wire. In operation of the transmitter the signal received bytransistor 110 is amplified in power through the amplifier 70 and isradiated from the induction loop 116. The radiation from the loop 116 isprimarily at the audio frequencies transmitted.

In operation of the model automobile 18 illustrated in FIGS. 1 and 2 theinduction loop 116 may be laid out in a fifty foot diameter circle oraround the periphery of a room and will provide sufficient poweranywhere within the induction loop to operate steering motor 16 on themodel automobile 18 through reception of the transmitted electromagneticsignal from the transmitter 10 by the receiver 12. Care should be takennot to include reentrant portions in the induction loop which woulddistort the field strength within the loop. Further, due to the use ofthe magnetic induction field rather than the electric induction field inboth the transmitter 10 and receiver 12 the transmitter is efficient andthe receiver is selective whereby a plurality of models may be operatedwithin the same area or room. Such selective operation is not possibleat audiofrequencies with apparatus as simple, economical and efficientas that herein disclosed if the transmitted radiation field is used formodel control due to the length ofa tuned antenna required withradiation fields at such frequencies. The electromagnetic powertransmitted from induction loop 116 and picked up by resonant circuit118 is not similarly dependent on antenna length.

The receiver 12, as shown best in FIG. 5, includes the tuned magneticinduction pickup circuit 118, audio amplifiers 1211 and 122,amplifier-rectifier 124 and power supply 126 consisting of two one andone-half volt direct current batteries 128 and 1311 in series.

The magnetic induction audiofrequcncy pickup circuit 118 includes a coil132 having a permeable ferrite core 134 operably associated therewithand the tuning capacitor 136. Thus, the pickup circuit 118 isparticularly responsive to the electromagnetic rather than theelectrostatic field radiated from the induction loop 116 of thetransmitter 10. Further, inasmuch as the pickup circuit 118 is tuned toresonate at the predetermined frequency of transmitter 10 much greaterpower reception by receiver 12 from transmitter 10 is possible thanwould be possible if the pickup circuit were not tuned.

Audio amplifier 120 includes transistor 138 having emitter, base andcollector elements 140, 142 and 144 respectively, a biasing networkincluding resistors 146 and 148 connected in a voltage divider circuitacross the power supply 126, the resistor 150 in the emitter circuit ofthe transistor 138, bypass capacitor 152 and load resistor 154.Amplifier 138 serves to amplify the power of the electromagneticaudiofrequency signal received by the pickup circuit 118 and isconnected with the pickup circuit across the emitter base thereof, asshown in FIG. 5.

Amplifier 122 includes the transistor 156 having the emitter, base andcollector elements 158, 160 and 162 respectively, the coupling resistorand capacitor 164 and 166 respectively, and the primary winding 168 ofthe coupling transformer 170. The amplified signal received fromamplifier 138 through the resistance-capacitance coupling circuit byamplifier 156 is again amplified in the amplifier 156 and is coupled tothe rectifier-amplifier 124 by means of the secondary winding 172 of thecoupling transformer 170.

The rectifier-amplifier circuit 124 includes the transistor 174 havingthe emitter, base and collector elements 176, 178

and 180 respectively, filter capacitor 182 and relay load coil 62connected, as shown in FIG. 5. Rectifier-amplifier 124 serves to againamplify the signal received from amplifier circuit 122, rectifies theamplified signal and operates relay 54, as previously indicated, on asignal being received by the tuned circuit 118 from transmitter 10.

Thus, in overall operation of the model automobile 18 with thetransmitter 10, receiver 12, drive motor 22, and steering motor 16, thetransmitter is placed in the area in which it is desired to operate themodel automobile with the induction loop extending around the area,suchas around the periphery of a room. The model automobile is placedwithin the induction loop 116 and the switch 140 to the drive motor 22and receiver power on-off switch 181 are closed. At this time theautomobile 18 will run in a circle with the steering motor at one limitof its operation. The direction of turning of the automobile 18 will bedetermined by the direction in which the drive motor is connected withthe relay 54 no energized. Suitable limit switches (not shown) can beused to limit the operation of the motor 16 if considered desirable.However, with the small motors and low power contemplated the limit ofmechanical movement of bellcrank 46 determines the steering limits.

The transmitter 10 is then energized through closing the switch 186 atwhich time the transmitter 10 will transmit an electromagnetic signal ata frequency of for example l.5 kilocycles or 9 kilocycles. Thetransmitted signal will be picked up by the magnetic induction pickupcircuit 118 of the receiver 12 and the relay 54 will be energized toreverse the direction of energizing the reversible steering motor 16 tocause the automobile to change the direction of movement thereof. Bytiming the opening and closing of the transmitter switch 186 completesteering of the automobile 18'may be accomplished.

If opening and closing of the transmitter switch 186 is consideredobjectionable an electronic pulsing circuit 26, such as that illustratedin FIG. 6, may be included in the transmitter 10. The electronic pulsingcircuit 26, as illustrated in H6. 6, may be connected in the transmittercircuit 10 by providing a relay armature 188 in the conductor betweenthe emitter 112 of transistor 111) and the induction loop 116 so as toalternately make or break the connection between the emitter 112 andinduction loop 116 depending on whether or not the coil 1% of relay 192is energized.

The electronic pulsing circuit comprises a free running multivibrator194 connected across the power supply 72 through conductors 196 and 198.'Multivibrator 194 is conventional and includes the transistors 200 and202, capacitors 204 and 206 and resistors 208, 210 and 212 connected, asshown in FIG. 6. Load resistor 214 is provided in conjunction withtransistor 200 while the load for transistor 202 includes the rectifier216 and relay coil 190 in parallel. The resistor 210 includes thevariable position wiper arm 218 as shown.

Thus in operation with theelectronic pulsing circuit 26 the transmitteris turned on with switch 186 and switch 186 is left closed. Thus, withthe wiper arm 218 centered on resistor 210 the output signal fromtransmitter 10 will be equally divided between on and off times sincethe multivibrator 194 is designed to operate in this manner with thewiper arm 218 centered. in other words, the relay 192 will be energizedonehalf of the time during operation of the multivibrator 194 so thatthe induction loop 116 will be connected to the emitter 112 one-half ofthe time.

To vary the direction of steering of the automobile 18. with theelectronic pulsing circuit the wiper arm 218 is moved in one directionor the other from center to vary the conducting time of the transistor202 in the multivibrator circuit 194 and thus the closed time of therelay 192.

While one embodiment of the audiofrequency selective, magnetic inductioncoupled, remote control system of the invention-has been considered indetail, other embodiments and modifications thereof are contemplated.Thus control of many other items, both model and full size, may beeffected through use of the extremely simple, economical and efficientreceiver and transmitter which are magnetically coupled as disclosedherein. Further, it will be readily understood that aplurality of othercontrols could be effected in the automobile or other models through theuse of the magnetically coupled frequency selective transmittersoperating at audiofrequencies below kilocycles. Also, it will beunderstood that the transmitter and receiver disclosed may be used forother than remote control systems. Thus short distance communicationsystems, such as are used by skin divers, may advantageously include theprinciples of the invention. Further, while the transmitter and receiverdisclosed have particular advantage operating at audiofrequency, theinvention is not so limited. It is intended to include all suchmodifications and embodiments as are defined by the appended claimswithin the scope of the invention.

lclaim:

1, A remote control system for models comprising an audiofrequencyinduction loop generated magnetic induction wave transmittingtransmitter including a transmitter power supply, an audiofrequencyoscillator including an oscillator transistor having emitter, base andcollector elements, an emitter resistor connected between one side ofthe power supply and the oscillator transistor emitter, a transmittervoltage divider network connected between the opposite sides of thetransmitter power supply, a feedback coil connected between the base ofthe oscillator transistor and a point on the transmitter voltage dividernetwork and a resistance and tuned circuit operably associated with thetuned circuit connected in series between the collector of theoscillator transistor and a second point on the transmitter voltagedivider network, a first transmitter amplifier including an amplifiertransistor having emitter, base and collector electrodes, meansconnecting the collector electrode of the amplifier transistor to theone side of the transmitter power supply, means connecting the base ofthe amplifier transistor to the tuned circuit and a resistor connectedbetween the one side of the transmitter power supply and the emitter ofthe amplifier transistor whereby the amplifier transistor is connectedin emitter follower configuration, and a second amplifier transistorhaving emitter, base and collector electrodes, means for connecting thecollector electrode of the second amplifier transistor to the other sideof the power supply, means for connecting the base of the secondamplifier transistor to the emitter of the'first amplifier transistorand a magnetic induction loop antenna encomconnected in parallel, areciever power supply, a series receiver amplifier for receiving thesignal from the pickup circuit and amplifying it including emitter, baseand collector electrodes, a collector resistor connected in seriesbetween one side of the reciever power supply and the collectorelectrode of the receiver amplifier transistor, an emitter resistorconnected between the emitter of the receiver amplifier transistor andthe other side of the receiver power supply, a voltage divider connectedbetween the opposite sides of the power supply, means connecting thebase of the receiver amplifier transistor to one side of the pickupcircuit, a capacitor connecting the emitter of the receiver amplifier toa point on the receiver voltage divider and means connecting the otherside of the pickup circuit to the same point on the receiver voltagedivider, a second amplifier including a transistor having emitter, baseand collector electrodes, a transformer primarily winding connected inseries between the collector electrode of the second amplifier and theone side of the power supply, a resistor connected to the one side oftherectifier power supply and the second amplifier base, a capacitorconnected between the collector ofthe receiver amplifier and the secondamplifier base, and means connecting the emitter of the second amplifierto the other side of the power supply and a reciever power amplifierrectifier including a transistor having emitter, base and collectorelectrodes, means connecting the base electrode of the amplifierrectifier through the secondary winding of the transformer to the otherside of the receiver power supply, means connecting the emitter of the'receiver power amplifier to the other side of the receiver powersupply, a capacitor connected between the collector of the receiverpower amplifier and the other side of the receiver power supply, a relaycoil connected between the receiver power supply and the amplifierrectifier collector and means connected to the receiver for controllingthe model in response to the magnetic induction wave transmitted by thetransmitter to the receiver including a reversible motor, a power sourcefor energizing said motor and means for energizing the steering motor inaccordance with the energy through the relay coil of the receiveramplifier rectifier circuit.

2. Structure as set forth in claim 1 and further including means forenergizing and deenergizing the magnetic induction loop antenna forpulsing the output of the transmitter comprising a free-runningmultivibrator connected across the transmitter power supply andincluding a relay having the coil as the load on one side thereof and aswitching armature responsive to the coil in series with the emittercollector cir cuit ofthe receiver power amplifier.

3. Structure as set forth in claim 2 wherein the means connected to thereceiver for controlling the model further includes an arm connected tothe steering motor for rotation thereby, a steering wheel, a verticalpivot mounting the steering wheel on the model, means for moving thesteering wheel about the vertical pivot in accordance with rotationofthe arm by the steering motor and resilient means for urging thesteering wheel to a central position about the pivot mounting therefor.

1. A remote control system for models comprising an audiofrequencyinduction loop generated magnetic induction wave transmittingtransmitter including a transmitter power supply, an audiofrequencyoscillator including an oscillator transistor having emitter, base andcollector elements, an emitter resistor connected between one side ofthe power supply and the oscillator transistor emitter, a transmittervoltage divider network connected between the opposite sides of thetransmitter power supply, a feedback coil connected between the base ofthe oscillator transistor and a point on the transmitter voltage dividernetwork and a resistance and tuned circuit operably associated with thetuned circuit connected in series between the collector of theoscillator transistor and a second point on the transmitter voltagedivider network, a first transmitter amplifier including an amplifiertransistor having emitter, base and collector electrodes, meansconnecting the collector electrode of the amplifier transistor to theone side of the transmitter power supply, means connecting the base ofthe amplifier transistor to the tuned circuit and a resistor connectedbetween the one side of the transmitter power supply and the emitter ofthe amplifier transistor whereby the amplifier transistor is connectedin emitter follower configuration, and a second amplifier transistorhaving emitter, base and collector electrodes, means for connecting thecollector electrode of the second amplifier transistor to the other sideof the power supply, means for connecting the base of the secondamplifier transistor to the emitter of the first amplifier transistorand a magnetic induction loop antenna encompassing the area in which themodel is to be controlled connected in series between the emitter of thesecond amplifier transistor and the one side of the transmitter powersupply, an audiofrequency induction wave receiving receiver primarilymagnetic induction coupled to said transmitter mounted in the modelincluding a frequency selective magnetic pickup circuit tuned to thesame audiofrequency as the transmitter transmits and comprising a coilhaving a permeable core and a capacitor connected in parallel, areciever power supply, a series receiver amplifier for receiving thesignal from the pickup circuit and amplifying it including emitter, baseand collector electrodes, a collector resistor connected in seriesbetween one side of the reciever power supply and the collectorelectrode of the receiver amplifier transistor, an emitter resistorconnected between the emitter of the receiver amplifier transistor andthe other side of the receiver power supply, a voltage divider connectedbetween the opposite sides of the power supply, means connecting thebase of the receiver amplifier transistor to one side of the pickupcircuit, a capacitor connecting the emitter of the receiver amplifier toa point on the receiver voltage divider and means connecting the otherside of the pickup circuit to the same point on the receiVer voltagedivider, a second amplifier including a transistor having emitter, baseand collector electrodes, a transformer primarily winding connected inseries between the collector electrode of the second amplifier and theone side of the power supply, a resistor connected to the one side ofthe rectifier power supply and the second amplifier base, a capacitorconnected between the collector of the receiver amplifier and the secondamplifier base, and means connecting the emitter of the second amplifierto the other side of the power supply and a reciever power amplifierrectifier including a transistor having emitter, base and collectorelectrodes, means connecting the base electrode of the amplifierrectifier through the secondary winding of the transformer to the otherside of the receiver power supply, means connecting the emitter of thereceiver power amplifier to the other side of the receiver power supply,a capacitor connected between the collector of the receiver poweramplifier and the other side of the receiver power supply, a relay coilconnected between the receiver power supply and the amplifier rectifiercollector and means connected to the receiver for controlling the modelin response to the magnetic induction wave transmitted by thetransmitter to the receiver including a reversible motor, a power sourcefor energizing said motor and means for energizing the steering motor inaccordance with the energy through the relay coil of the receiveramplifier rectifier circuit.
 2. Structure as set forth in claim 1 andfurther including means for energizing and deenergizing the magneticinduction loop antenna for pulsing the output of the transmittercomprising a free-running multivibrator connected across the transmitterpower supply and including a relay having the coil as the load on oneside thereof and a switching armature responsive to the coil in serieswith the emitter collector circuit of the receiver power amplifier. 3.Structure as set forth in claim 2 wherein the means connected to thereceiver for controlling the model further includes an arm connected tothe steering motor for rotation thereby, a steering wheel, a verticalpivot mounting the steering wheel on the model, means for moving thesteering wheel about the vertical pivot in accordance with rotation ofthe arm by the steering motor and resilient means for urging thesteering wheel to a central position about the pivot mounting therefor.